 /*******************************************************************************
  * Copyright (c) 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.osgi.internal.verifier;

 public class Base64 {

     private static final byte equalSign = (byte) '=';

     static char digits[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', //
 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', //
 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', //
 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'};

     /**
      * This method decodes the byte array in base 64 encoding into a char array
      * Base 64 encoding has to be according to the specification given by the
      * RFC 1521 (5.2).
      *
      * @param data the encoded byte array
      * @return the decoded byte array
      */
     public static byte[] decode(byte[] data) {
         if (data.length == 0)
             return data;
         int lastRealDataIndex = data.length - 1;
         while (data[lastRealDataIndex] == equalSign)
             lastRealDataIndex--;
         // original data digit is 8 bits long, but base64 digit is 6 bits long
 int padBytes = data.length - 1 - lastRealDataIndex;
         int byteLength = data.length * 6 / 8 - padBytes;
         byte[] result = new byte[byteLength];
         // Each 4 bytes of input (encoded) we end up with 3 bytes of output
 int dataIndex = 0;
         int resultIndex = 0;
         int allBits = 0;
         // how many result chunks we can process before getting to pad bytes
 int resultChunks = (lastRealDataIndex + 1) / 4;
         for (int i = 0; i < resultChunks; i++) {
             allBits = 0;
             // Loop 4 times gathering input bits (4 * 6 = 24)
 for (int j = 0; j < 4; j++)
                 allBits = (allBits << 6) | decodeDigit(data[dataIndex++]);
             // Loop 3 times generating output bits (3 * 8 = 24)
 for (int j = resultIndex + 2; j >= resultIndex; j--) {
                 result[j] = (byte) (allBits & 0xff); // Bottom 8 bits
 allBits = allBits >>> 8;
             }
             resultIndex += 3; // processed 3 result bytes
 }
         // Now we do the extra bytes in case the original (non-encoded) data
 // was not multiple of 3 bytes
 switch (padBytes) {
             case 1 :
                 // 1 pad byte means 3 (4-1) extra Base64 bytes of input, 18
 // bits, of which only 16 are meaningful
 // Or: 2 bytes of result data
 allBits = 0;
                 // Loop 3 times gathering input bits
 for (int j = 0; j < 3; j++)
                     allBits = (allBits << 6) | decodeDigit(data[dataIndex++]);
                 // NOTE - The code below ends up being equivalent to allBits =
 // allBits>>>2
 // But we code it in a non-optimized way for clarity
 // The 4th, missing 6 bits are all 0
 allBits = allBits << 6;
                 // The 3rd, missing 8 bits are all 0
 allBits = allBits >>> 8;
                 // Loop 2 times generating output bits
 for (int j = resultIndex + 1; j >= resultIndex; j--) {
                     result[j] = (byte) (allBits & 0xff); // Bottom 8
 // bits
 allBits = allBits >>> 8;
                 }
                 break;
             case 2 :
                 // 2 pad bytes mean 2 (4-2) extra Base64 bytes of input, 12 bits
 // of data, of which only 8 are meaningful
 // Or: 1 byte of result data
 allBits = 0;
                 // Loop 2 times gathering input bits
 for (int j = 0; j < 2; j++)
                     allBits = (allBits << 6) | decodeDigit(data[dataIndex++]);
                 // NOTE - The code below ends up being equivalent to allBits =
 // allBits>>>4
 // But we code it in a non-optimized way for clarity
 // The 3rd and 4th, missing 6 bits are all 0
 allBits = allBits << 6;
                 allBits = allBits << 6;
                 // The 3rd and 4th, missing 8 bits are all 0
 allBits = allBits >>> 8;
                 allBits = allBits >>> 8;
                 result[resultIndex] = (byte) (allBits & 0xff); // Bottom
 // 8
 // bits
 break;
         }
         return result;
     }

     /**
      * This method converts a Base 64 digit to its numeric value.
      *
      * @param data digit (character) to convert
      * @return value for the digit
      */
     static int decodeDigit(byte data) {
         char charData = (char) data;
         if (charData <= 'Z' && charData >= 'A')
             return charData - 'A';
         if (charData <= 'z' && charData >= 'a')
             return charData - 'a' + 26;
         if (charData <= '9' && charData >= '0')
             return charData - '0' + 52;
         switch (charData) {
             case '+' :
                 return 62;
             case '/' :
                 return 63;
             default :
                 throw new IllegalArgumentException ("Invalid char to decode: " + data); //$NON-NLS-1$
 }
     }

     /**
      * This method encodes the byte array into a char array in base 64 according
      * to the specification given by the RFC 1521 (5.2).
      *
      * @param data the encoded char array
      * @return the byte array that needs to be encoded
      */
     public static byte[] encode(byte[] data) {
         int sourceChunks = data.length / 3;
         int len = ((data.length + 2) / 3) * 4;
         byte[] result = new byte[len];
         int extraBytes = data.length - (sourceChunks * 3);
         // Each 4 bytes of input (encoded) we end up with 3 bytes of output
 int dataIndex = 0;
         int resultIndex = 0;
         int allBits = 0;
         for (int i = 0; i < sourceChunks; i++) {
             allBits = 0;
             // Loop 3 times gathering input bits (3 * 8 = 24)
 for (int j = 0; j < 3; j++)
                 allBits = (allBits << 8) | (data[dataIndex++] & 0xff);
             // Loop 4 times generating output bits (4 * 6 = 24)
 for (int j = resultIndex + 3; j >= resultIndex; j--) {
                 result[j] = (byte) digits[(allBits & 0x3f)]; // Bottom
 // 6
 // bits
 allBits = allBits >>> 6;
             }
             resultIndex += 4; // processed 4 result bytes
 }
         // Now we do the extra bytes in case the original (non-encoded) data
 // is not multiple of 4 bytes
 switch (extraBytes) {
             case 1 :
                 allBits = data[dataIndex++]; // actual byte
 allBits = allBits << 8; // 8 bits of zeroes
 allBits = allBits << 8; // 8 bits of zeroes
 // Loop 4 times generating output bits (4 * 6 = 24)
 for (int j = resultIndex + 3; j >= resultIndex; j--) {
                     result[j] = (byte) digits[(allBits & 0x3f)]; // Bottom
 // 6
 // bits
 allBits = allBits >>> 6;
                 }
                 // 2 pad tags
 result[result.length - 1] = (byte) '=';
                 result[result.length - 2] = (byte) '=';
                 break;
             case 2 :
                 allBits = data[dataIndex++]; // actual byte
 allBits = (allBits << 8) | (data[dataIndex++] & 0xff); // actual
 // byte
 allBits = allBits << 8; // 8 bits of zeroes
 // Loop 4 times generating output bits (4 * 6 = 24)
 for (int j = resultIndex + 3; j >= resultIndex; j--) {
                     result[j] = (byte) digits[(allBits & 0x3f)]; // Bottom
 // 6
 // bits
 allBits = allBits >>> 6;
                 }
                 // 1 pad tag
 result[result.length - 1] = (byte) '=';
                 break;
         }
         return result;
     }
 }
